I throw putters around the yard for practice. Between the back yard and front (and a little of the neighbor's yard) I can choose a variety of lines and elevations. The longest throw is about 220' uphill, with enough trees and bushes to make it interesting. I move the practice basket around to practice different lines.

My favorite practice throw involves hitting a gap between the house and a huge pin oak and then making a controlled turn downhill to land near the stop sign on the corner, with the road as OB. It's a fun shot forehand or backhand.

To practice with midranges or drivers I throw hyzers down the street, fading into the neighbor's front lawn. Fortunately all of my neighbors are pretty tolerant of (and, I suspect, entertained by) that fool throwing frisbees in the yard.

A lot of people have mentioned the soccer fields, but no one has mentioned using the soccer goal net itself. That's pretty fun for practice as well.

I do use soccer goals as targets for long drives, but holes on those nets are usually way too big to keep discs in(just enough to keep the ball from going through) so I wouldn't recommend to use them as driving nets. Dunno if there's an official size for those holes tho.

A net is not a replacement for field work, but a supplement to it. If you buy some new discs and want to get a feel for them, go to the field. If you want to work on your throw, a net may be the trick. I'm working on my left handed throws right now, and the net is perfect. I still have about 1/5 throws that aren't anywhere close to where I want them to go, and I'm trying to eliminate those. The cage I throw at has proper dimensions that the disc will hit the wrong wall/ceiling if I throw one that badly.

Just like there's no replacement for seeing a disc fly, there's no replacement for 300 throws/hour.

Also, with a little imagination and prediction, I have a good idea where my disc would have ended up.